Optoelectronic devices are often fabricated from Group-III-V elements. Examples include light emitting diodes (LED) fabricated from gallium nitride (GaN). The formation of ohmic contacts to optoelectronic devices is challenging due to the properties of the materials and the surface reactions. Further, ohmic contact schemes must be developed for both n-type and p-type optoelectronic materials.
Generally, the requirements for the ohmic contact materials in an optoelectronic device include good adhesion, low contact resistance, high reflectivity, good thermal stability, and good chemical stability. Other desirable attributes include that the material should be refractory and that the material forms stable nitride compounds.
The requirements and attributes listed above cannot be achieved by a single material. Therefore, the ohmic contacts to optoelectronic devices are typically manufactured as stacks of different layers. The interaction of these layers with and their interaction with the substrate further complicate the development and optimization of the ohmic contact stack.
The development of ohmic contact stacks for optoelectronic devices is largely an empirical task, wherein materials, process parameters, process sequences, and post deposition treatment processes must be evaluated without the benefit of predictive theory. Due to the complexity of the ohmic contact stacks, the number of experiments, time, and cost of the endeavor is daunting. There is a need for efficient methods for screening and evaluating the materials, process parameters, process sequences, and post deposition treatment processes for the development of ohmic contact stacks for optoelectronic devices.